1. Field of the Invention
The present invention relates to a pneumatic radial tire, and in particular, to a pneumatic radial tire which is suitable for airplanes, and to which heavy loads are applied, and which are subjected to high speed traveling.
2. Description of the Related Art
In recent years, airplane manufacturers have promoted the development of extremely large passenger airplanes, and demands with respect to increasing the size and durability of tires therefor have, of necessity, become severe.
In order to ensure good durability which satisfies these demands, it is essential to increase the number of plies of the carcass in the tire structure. However, when the number of plies of the carcass increases, the bead core is located away from the bead base face, and the rim tends to line-contact the tire at the bead base face. As a result, there arises a problem in that drawbacks such as cracking of the bead base face are more likely to occur due to local stress concentration and in that the durability of the bead portion deteriorates.
A pneumatic radial tire having a plurality of bead cores within the bead portion has been proposed as a pneumatic radial tire for large passenger airplanes. An example of such a pneumatic radial tire for airplanes is the pneumatic radial tire disclosed in Japanese Patent Application (JP-A) No. 9-175108.
In the case of this example, there are problems in that the structure becomes complex and costs increase, due to the provision of a crescent-shaped rubber layer. In addition, when the tire is made large and the number of radial carcass plies is increased, as described above, the rim tends to line-contact the tire at the bead base face, and a deterioration in durability of the bead portion is unavoidable.
In view of the aforementioned facts, an object of the present invention is to provide a pneumatic radial tire in which, even if the tire is large and the load that the tire bears is large, durability of the bead portion can be ensured.
In order to achieve the above-described object, in a first aspect of the present invention, a pneumatic radial tire comprises: a bead portion provided with a plurality of bead cores; and one or plural radial carcass plies which are wound up from a tire inner side toward an outer side at the respective bead cores, wherein one-half or more of the number of end portion(s) of the radial carcass ply (plies) is/are positioned at each bead core within a range of 35 to 55% of a tire section height as measured from the reference line of the tire section height. Here, xe2x80x9cthe reference linexe2x80x9d is defined as a reference line which is parallel to the tire rotation axis, and passes through an intersection of a straight line passing through the bead sheet and an imaginary line extended from the inner wall surface of the rim flange which imaginary line is perpendicular to the tire rotation axis.
In accordance with the pneumatic radial tire of the first aspect, the following effects are achieved.
One-half or more of the number of end portion(s) of the radial carcass ply (plies) wound up on the bead cores is/are disposed at each bead core within a range of 35 to 55% of a tire section height as measured from the reference line of the tire section height. Thus, the rigidity from the bead portion to the side (wall) portion increases, deformation of the bead portion in a loaded state is suppressed, and the strain level of the bead portion can be reduced. In this way, durability of the bead portion is improved.
If one-half or more of the number of end portion(s) of the radial carcass ply (plies) wound up on the bead cores is/are disposed at positions which are less than 35% of the tire section height as measured from the reference line of the tire section height, it is difficult to suppress deformation of the bead portion in a loaded state.
On the other hand, if one-half or more of the number of end portion(s) of the radial carcass ply (plies) wound up on the bead cores is/are disposed at positions which exceed 55% of the tire section height as measured from the reference line of the tire section height, the end portions are positioned at each bead core at the portion of the tire side portion where strain is great, and separation is more likely to occur.
In a second aspect of the present invention, in the pneumatic radial tire of the first aspect, end portions of radial carcass plies, which are among the radial carcass plies wound up from the tire inner side toward the outer side and which are not positioned within the range of 35 to 55% of the tire section height as measured from the reference line of the tire section height, are positioned at an inner side than an outermost end of a rim flange in the radial direction.
In accordance with the pneumatic radial tire of the second aspect, the following effects are achieved.
The end portions of radial carcass plies, which are not positioned within the range of 35 to 55% of the tire section height as measured from the reference line of the tire section height, are positioned at an inner side than an outermost end of a rim flange in the radial direction, i.e., are positioned at a region where strain is relatively little (the strain therein is relatively little because the region is supported by the rim flange). Therefore, separation which is generated from the ply ends can thereby be suppressed.
In a third aspect of the present invention, in the pneumatic radial tire of the first or second aspect, end portions of radial carcass plies which are wound up at a bead core located at an outermost side in the tire axial direction are positioned within the range of 35 to 55% of the tire section height as measured from the reference line of the tire section height.
In accordance with the pneumatic radial tire of the third aspect, the following effects are achieved.
In the bead portion, strain at the time of bearing a load tends to concentrate in the vicinity of the rim flange. Accordingly, by positioning end portions of radial carcass plies, which are wound up at the bead core at the outermost side in the tire axial direction near the rim flange, in a range of 35 to 55% of the tire section height as measured from the reference line of the tire section height, i.e., by setting these end portions of the radical carcass plies at the outer side than the portion at which strain concentrates, in the tire radial direction, separation which is generated from the ply ends can be significantly suppressed.